This invention relates to method and apparatus for performing power conversion. More specifically, it relates to method and apparatus for performing AC/DC conversion to provide a regulated DC output with reduced distortion of the input supply waveform.
Existing AC/DC conversion techniques distort the AC supply waveform as a result of harmonic feedback to the AC supply. Such distortion in the AC supply waveform can affect the use of the AC supply by other loads. Furthermore, system power losses increase because of the useless harmonic power being supplied to the various loads.
As a result, many AC/DC converters require AC filters at their input to filter out the harmonic frequencies to try to minimize the distortion of the supply waveform. In prior art AC/DC converters, the first order harmonic, which has greater amplitude than the higher order harmonics and is therefore of particular interest, is typically a low-frequency signal, so that the input filters generally require heavy electromagnetic components. The input filters in prior art AC/DC generators, therefore, are large and heavy, thereby increasing the volume and expense of AC/DC converters.
Further, the large input filters typically have a large reactance. The phase between the fundamental components of the current and the voltage in the input AC supply is, therefore, shifted by the input filters. As a result, the power factor associated with the AC supply deteriorates. Capacitors are typically used in such cases to correct the power factor, however, this causes the weight and size of the converter to further increase and can create a resonance at existing harmonic frequencies.
Method and apparatus for AC/DC conversion that results in reduced distortion of the AC supply waveform and reduced power factor deterioration of the AC supply is, therefore, needed.